This invention relates to a bicycle with a power assist provided by an electric motor and more particularly an improved power assisted manually operated device.
A wide variety of devices have been proposed which are primarily manually operated but which provide a power assist. For example, it has been proposed to provide a bicycle which is pedal operated but which includes an electric motor that is operated so as to assist the pedal operation in proportion to the load exerted at the pedals. Such devices have particular utility but do have some disadvantages.
The electric motor is normally coupled to the driven wheel of the bicycle through a one-way clutch. The one-way clutch is employed so as to accommodate the situation when the motor speed is low or below the actual speed of the bicycle. This condition can exist during a number of circumstances, for example when the traveling down hill or during a condition as will be described.
In conjunction with a bicycle, the pedal operator is normally a crank mechanism and the output force applied by the operator to the pedals varies with the angular position of the pedals. At top and bottom dead centers, no significant propulsion forces are accomplished but as the crank moves between these positions, then a driving force is provided. Because of this mechanism, the power assist, when called for, has a tendency to lag behind the actual demand requirements.
This may be understood by reference to FIG. 1 wherein the solid line curve shows the pedal force in relation to time. A complete cycle of rotation of the pedal is shown and it will be seen that when the pedal is at top dead center, no significant force is applied and as the pedal moves toward bottom dead center, the force will increase and then gradually decrease as bottom dead center is approached. The force output cyclically varies during the next half cycle as seen in this figure. The pedal force depicted in the drawings F.sub.L provides a speed of the bicycle indicated by the line N.sub.O,
As a result of the affect of the pedal action, when the pedal moves to one dead center position the force exerted on the pedals will reach zero and the electric motor drive will be discontinued, even though the bicycle is still traveling at the speed N.sub.O. As the pedal moves past the dead center position, the force applied to the pedals will call for the increase of electric motor operation. However, the electric motor will not exerted any assist force until the speed of the electric motor reaches the speed at which the bicycle is traveling N.sub.O which gives rise of a time delay of "a" until the power assist comes into effect. As a result of this and as clearly seen in FIG. 1, each half revolution of the pedal mechanism, there will be a slow down and stoppage of the electric motor and then a time delay before the electric motor again assists in the operation. In addition to having a loss in the total amount of power assist, this also consumes excess electrical energy because of the starting and stopping of the electric motor.
It is, therefore, a principal object to this invention to provide an improved arrangement for providing a power assist to a manually operated device.
It is a further object to this invention to provide a power assist for a manually operated device wherein the power assist is always driven at a speed equivalent to that of the manually operated device so that when power assist is called for, the power assist need not be accelerated to that speed.